# Lesson 17 时间介词 before/during/after/within

今天我们要学习四个新的时间介词。首先通过以下系列图片了解一下 before、during 和 after 的区别。

![看电影前](images/vJzZ1wanDr.png)
- before the film 电影前
- during the film 电影中
- after the film 电影后

**before**：表示"在……之前"
- Everyone feels nervous before exams.
  每个人在考试前都会紧张。
- I like reading books before sleeping.
  我喜欢睡前阅读。

**during**：表示"在……之中"，强调过程

![看电视](images/glcY1wanDr.png)
- He often eats doughnuts during the TV show.
  他经常在看那个电视节目的时候吃甜甜圈。
- Don't sleep during the class.
  上课期间别睡觉。

**after**：表示"在……之后"
- I went home after one hour. 一小时后我就回家了。
- He finished his homework after dinner. 晚饭后他写完了作业。

**within**：表示"在……之内"
- You will receive the reply within seven days. 你会在7天之内收到答复。
- I have to finish my homework within two hours. 我必须在2小时内写完作业。

> **特别注意：within 与 during 的区别**
> - within + 时间段，表示"在……之内"
>   • within two days 两天内
>   • within three hours 三小时内
>   • within one week 一周内
> - during + 某件事，表示"在……期间"
>   • during the film
>   • during dinner 晚饭期间
>   • during the class 上课期间

### 本课小结

- before / during / after 在……之前/之中/之后
- within + 一段时间，在……内

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